GB2298493A - Floating projection head for high speed writer. - Google Patents

Description

FLOATING RADIANT ENERGY PROJECTION EMAD FOR HIGH SPEED WRITER

BACKGROUND OF THE INVENTION

2298493 Field of Invention

This invention relates to the field of photography, photolithographic processes and imaging systems, where light is scanned onto the surface of a sensitized media to produce an image.

Description of the Prior Art.

To form an image in a silver halide film or any other light sensitive media, light has to be directed onto the media with sufficient exposure power. At the same time, the light must be contained to only that portion of the media which is to be exposed. Numerous systems are known that use a remote, scanning light source and a series of fibers, optical paths, mirrors, and/or lenses to project the light onto a desired spot on the sensitized media. When the media is sensitized for color processing, three light sources, or three separate and independently modulated spectral bands, must be used.

For example, Figure 1 illustrates a noncoherent light source and a lens system for focusing that portion of the light emitted through a mask onto a receiver media. Light collection efficiency is poor, as a large percentage of the emitted light is not imaged through the lens and, therefore, does not reach the receiver media.

U.S. Patent No. 4,961,080, which issued to Henderson et al. on October 2, 1990, shows a scanning shaft system, where mirrors are positioned around the drum at fixed positions to reflect a laser beam onto the imaged surface. The mirrors t 2 - image through apertures in the drum-surface, to which the shaft is central., U.S. Patent No. 4,918,465, which issued to Morita on April 17, 1990, shows a system using three light sources to produce full color images. The light sources are remote from the image drum. Fiber optics are used to transmit the light to the sensitized material on the drum surface.

U.S. Patent No. 4,544,259, which issued to Kanaoka et al. on October 1, 1985, shows a system of colored light sources and a plurality of light guides. Numerous light sources of the same color are used to increase the amount of light energy available to increase the printing speed.

The light guide bundles have a lens system at the printing end to focus the light into a smaller spot.

U.S. Patent No. 4,797,691, which issued to Akiyoshi et al. on January 10, 1989, describes a side printing head assembly in which the light from an LED is guided to the printing region via a light guide.

U.S. Patent No. 4,907,034, which issued to Doi et al. on March 6, 1990, discloses a system to produce color images in a photosensitive media. Light is guided to the media from multiple sources by SELFOC lenses.

U.S. Patent No. 4,684,228, which issued to Holthusen on August 4, 1987, describes a laser beam photo-setting apparatus, wherein a mirror is used to direct a laser beam onto a media in a rotating drum.

U.S. Patent No. 4,479,133, which issued to Shiozawa et al. on October 23, 1984, describes a light beam rotary recorder having a rotor which - 3 houses light emitting sources. media is held in a semi-circular frame, and the rotor is translated over media by a lead screw.

SUIDUMY OF THE INVENTION It is an object of the present invention to provide a light beam rotary write head, which can effect recording with a high resolution and at a high recording speed. A highly efficient flying head system is provided which houses a light source or sources and allows the head to fly very small distances from the media without scratching it. The low flying height of the light source or sources above the sensitized media eliminates the need for lens systems to project the light, and therefore reduces optical energy losses in the system. Thus, less energy is required for the system to expose the media and less heat is produced to generate light of sufficient power.

According to the present invention, a write head is designed to effect a minimum spacing between the surface of a sensitized media and a floating head. The floating head is contoured to provide a self-acting air-bearing pressure to support the weight of the assembly and to balance the centrifugal forces exerted onto the floating head from the rotary motion of the media recorder.

The light source or sources are preferably mounted on a metal foil, which is laminated to other floating head structure. A hole in the foil above each light source allows light to egress from the source(s) and radiate directly onto the surface of the sensitized media. The distance between the light source(s) and the media surface is controlled by the floating head flying height and the foil thickness. The size and shape of the - 4 spot of light at the media is controlled by the distance of the hole in the foil from the media and by the hole's size and shape. Therefore the light conditions are precisely set by fixed physical attributes of the floating head.

In a preferred embodiment, the floating head is made from a ceramic material, which can be molded to final contoured shape to provide a strong, light weight structure. However, the floating head could be made from metals, plastics or composites of many materials. A heat sink provides a path for waste heat generated by the light source(s) to dissipate into the air flow around the head structure. The heat sink may be made from metal, typically copper.

The floating head may be mounted to an alignment structure such as a gimbal or flexure apparatus, which in turn is mounted onto a pivot arm attached to a rotor. As the rotor spins, the pivot arm allows centrifugal forces to move the head towards the media. The alignment structure allows the head to float and adjust for any irregularities in the media and drum surfaces. The head moves radially outwardly toward the media and floats on a cushion of air that is controlled similar to an airplane wing or a flying head in a hard disk.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which:

Figure 1 is a schematic illustration of a prior art exposure system;

Figure 2 is a schematic cross section through a printing apparatus having a floating head according to a preferred embodiment of the present invention; Figure 3 is a top view of the floating head of Figure 2, detailing a positive pressure air-bearing pocket and light source location; Figure 4 is a cross section through the floating head of Figure 3, showing a foil air dam, slot, heat sink, and light sources; Figure 5 is an enlarged view of a section of the printing apparatus showing the location of a light beam; Figure 6 shows the light beam impinging on the media, with a constant spacing air gap shown greatly enlarged for clarity; Figure 7 is a schematic illustration similar to Figure 1 showing the improved efficiency of apparatus according to the present invention; Figures 8a to 8d show the design curves to optimize a rectangular pocket geometry; Figures 9 and 10 illustrate a second preferred embodiment of the present invention; Figure 11 shows another embodiment of the present invention in which an LED package is attached to a cantilever- supported flexure alignment structure; and Figure 12 shows yet another embodiment of the present invention which is similar to that of Figure 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 2 shows a cross section of the printing apparatus with a wingshaped assembly for delivering light energy to a sensitized media. A floating head 10 is attached to an alignment structure such as a flexure 12. A gimbal alignment structure is described below with respect to another embodiment of the present invention. The alignment structure allows roll and pitch attitude adjustment of the floating head with respect to the forces exerted on it. A counterbalance weight 14 is attached to a pivot arm 16 opposed to floating head 10 and flexure 12. The pivot arm is attached to a rotor 18 at a pivot point 20. A tube-like member 22 having a cylindrical media support surface surrounds the rotor assembly. Media 24 is held to the support surface, such as by vacuum.

Figures 3 and 4 are top and side views, respectively, of floating head 10, formed of a ceramic body with overall breadth dimension B and length dimension L. Figure 4 is a sectional view taken along line 4-4 of Figure 3. A recessed pocket 26, which is shaded in Figure 3 for clarity, is formed in part by a slot in the aerodynamically contoured, curved surface of floating head 10 that will face the media support surface of member 22 in final assembly (Figure 2). In Figure 3, BI is the overall breadth dimension and Ll is length dimension.

A foil sheet 28, which is adhesively bonded into the slot, acts as an air dam in the slot to complete pocket 26. Air passing over the slot meets a dead end at the air dam and is forced upwards from this surface to provide a positive pressure above the curved surface of the floating head. Foil 28 has a plurality of holes 30 formed into the foil to allow light to pass through the foil. Foil sheet 28 has a height dimension hl-h2, where hl is the distance from the bottom of the slot forming pocket 26 to the emulsion surface of media 24 and h2 is the distance from the curved surface of the floating head to the emulsion surface of media. The light sources, which in the preferred embodiment are LED's 32, are shown under holes 30 cut in the foil. Beneath each LED is a copper head sink 34.

Figure 5 is a cross sectional view of the floating head assembly along line 5-5 in Figure 3. In the illustrated embodiment, the heat sink assembly is made from five pieces of copper. The three pieces 34 under the LED's are slightly shorter than the two outer pieces 36 to allow longer pieces 36 to bond to foil sheet 28. The copper pieces act both as heat sinks and as electrical connections. Heat sinks 34 are bonded to the LED's with solder or conductive polymers. This provides anode connection to LED's 32. Cathode connection to the LED's is between the diode and the foil sheet. Again, this connection is either, but not limited to, a solder joint or a conductive polymer. A cathode return to the underside of the floating head assembly is provided by copper pieces 36 on each end of the heat sink assembly. Cathodic heat sinks 36 are bonded to foil sheet 28 by either solder or conductive polymer. A sheet 38 of cloth or plastic inner core between each copper piece provides electrical insulation between the heat sinks. Electrical signal connection to the assembly is accomplished by soldering wires on the underside of the floating head to the individual heat sinks. A sheet 40 of, say, Kapton is bonded to the foil with adhesive and is fashioned to provide die alignment holes and electrical insulation between the LED's.

j 8 The heat sink/foil/LED ass emb ly is bonded to the ceramic floating head structure with adhesive material. Aperture holes 30 in foil sheet 28 are filled with an optically clear polymer to inhibit dust particles from obscuring the light sources.

Figure 6 shows an enlarged view of the floating head in relation to the media. The air gap is shown greatly enlarged for clarity. A light beam 42 is emitted from the floating head to expose the media. At the same time a positive pressurized air-bearing 44 is formed between the floating head and the media. As rotor 6 is rotated in the direction of an arrow 46, centrifugal forces are exerted on floating head 10. The floating head moves radially outwardly toward media 24, and the air passing between the floating head and the media is compressed to form a positive air-bearing. This allows the floating head to fly at a precise distance above the surface of media 24.

As best seen in Figure 7, the very close distance between the light source mask and the media minimizes optical losses by optimizing the optical spot size and shape as compared to the prior art structure of Figure 1. More light is collected at the media surface without requiring'a lens and its associated light losses. Hence, less power is dissipated to produce an effective amount of light in the writing spot. Also, because of the media proximity, no lens system is required to focus the light. The light spot size is controlled by the spacing of the floating head from the media 13, and the aperture size. Without a lens system, the floating head.is lighter and less costly to produce. The low mass of the floating head also 1 3 permits it to accurately track irregularities in, and eccentricities of, the writing surface.

The air-bearing pressure generated by the relative motion of the moving floating head and the stationary media must support the centrifugal forces acting on the floating head to maintain the prescribed spacing between the floating head and the media. The geometry of floating head pocket 26, as shown in Figure 3, can be optimized for a particular head configuration and speed. The pocket geometry can be rectangular or trapezoidal, in which the pocket narrows from the leading edge to the air dam wall. The pocket depth can also be tapered with the minimum depth being at the air dam wall and the maximum depth being at the leading edge of the floating head. The taper and trapezoid both offer slight increases in the bearing load capacity, with increased manufacturing difficulty.

The load bearing optimization is described for the simpler uniformly deep rectangular pocket, as shown in Figure 3, with the procedure being similar for the taper and the trapezoid. The optimization is performed using a numerical solution of the well known Reynolds lubrication equation, which governs the pressure developed between surfaces, when one is moving rapidly relative to the other, as is the case with the slider and media. In the analysis, five dimensionless parameters affect the performance of the bearing. They are derived from the actual geometry of the slider and the desired spacing between the slider and the media, and are shown in Figures 3, 4, and 6. The five dimensionless parameters are:

- 10 1) Bl/B, where B is the total breadth of the slider and B1 is the total breadth of the pocket; 2) Lj/L, where L is the total length of the slider and LI is the total length of the pocket; 3) hl/h2, where h2 is the desired slider-to-media spacing and hl-h2 is the pocket depth; 4) B/L, the breadth-to-length ratio of the slider; and 5) A = 6gUB/h2Pa, where A is the dimensionless bearing number, which includes the effect of the relative speed U, the viscosity of the air ji, and the atmospheric pressure Pa.

Another dimensionless bearing number AL can be defined, where:

AL = AL/B = 6gUL/h2Pa, and the dimensionless bearing load W', where W' = W/BLPa, with W being the actual bearing load. Knowledge of the dependence of W' on the five dimensionless parameters is all that is required to optimize the slider geometry for maximum bearing load.

Figure 8a shows the dependence of the 25 non-dimensional load on breadthto-length ratio (B/L) for the three values of AL 0.35, 0.55, and 1.

The figure illustrates that, for a range of slider speeds and a fixed slider length, the maximum bearing load occurs when the slider breadth-tolength ratio is 2.8. The graph assumes:

hl/h2 = 3.5, B1/B = 0.75, and Ll/L = 0.7.

Equipped with knowledge of the optimum value of B/L, one can proceed to optimize the other variables. Figure 8b shows the dependence of the dimensionless bearing load on the pocket breadth ratio (Bl/B), for AL - 0. 35, 0.55, and 1. The optimum occurs at Bl/B=0.84. The graph assumes hl/h2 = 3.5, B/L = 2.8, and Ll/L = 0 7, Figure 8c shows the dependence of the dimensionless bearing load on the pocket length 16 ratio (Ll/L), for AL 0.35, 0.55, and 1. The optimum occurs at Ll/L=0.675. The graph assumes:

h11h2 = 3.5, B/L = 2.8, and Bl/B = 0.84.

Figure 8d shows the dependence of the dimensionless bearing load on the media thickness ratio (Hl=hl/h2), for AL = 0.35, 0.55 and 1. The optimum occurs at H1=3.5. The graph assumes:

Ll/L = 0.675, B/L = 2.8, and Bl/B = 0. 84.

To apply this knowledge, consider a slider design, for example, where the system is constrained to having the light source 0.5 mils from the media and a slider of breadth of one inch. Thus, h2=0.0005 inch and B=l inch From the above, h1=1.75 mils; giving a pocket depth of 1.25 mils. The slider length is L=0.3570, since B/L is 2.8. The pocket length is Li=0. 2418, since Ll/L is 0.675. The pocket breadth is B1=0.84N, since Bl/B is 0.84. This completely defines the slider geometry. The actual bearing load can be extrapolated from Figure 8d, knowing the slider speed, air viscosity and ambient atmospheric pressure.

In addition, Figure 8 shows how sensitive the air-bearing load is to tolerances in the floating head geometric parameters. The air-bearing pressure generated must support the centrifugal forces acting on the floating head and maintain the prescribed spacing between the floating head mask and the media.

Figures 9 and 10 illustrate a second preferred embodiment of the present invention. A floating head 50 is attached to a gimbal alignment structure 52. The gimbal alignment structure allows roll, pitch, and yawl attitude adjustment of the floating head with respect to the forces exerted on it. A counterbalance weight 54 is attached to a pivot arm 56 opposed to floating head 50 and gimbal alignment structure 52. The pivot arm is attached to a rotor 58 at a pivot point 60. A tube-like member 62 having a cylindrical media support surface surrounds the rotor assembly. Media 64 is held to the support surface, such as by vacuum.

Gimbal alignment structure 52 includes an attachment arm 66 which has a socket for receiving a gimbal head 68 held in the socket-by a spring clip 70. An elastomer pad 72 damps movement of floating head relative to attachment arm 66.

Pivot arm 56 is urged in a counter clockwise direction about pivot point 60 by a pivot A light beam is emitted fro LED's 76 spring 74. on the floating head to expose the media. At the same time a positive pressurized air-bearing is formed between the floating head and the media. As rotor 58 is rotated in the direction of an arrow 78, centrifugal forces are exerted on floating head 50 in opposition to the force of pivot spring 74 and adjustable counterbalance 54. The floating head moves radially outwardly toward media 64, and the air passing between the floating head and the media is compressed to form a positive air-bearing. This allows the floating head to fly at a precise distance above the surface of media 64. Figures 11 and 12 illustrate two additional embodiments of the present invention. In Figure 11, an LED package 80 is attached to a cantilever-supported flexure alignment structure 82. The alignment structure allows roll and pitch attitude adjustment of the LED package with respect to the forces exerted on it. The alignment structure is attached to a rotor 84. A tube-like member 86 having a cylindrical media support surface surrounds the rotor. Media 64 is held to the support surface, such as by vacuum. 30 A positive pressurized air-bearing is formed between flexure alignment structure 82 and the media by an air pocket recess formed in the media-side surface of the alignment structure. As rotor 84 is rotated in the direction of an arrow 88, centrifugal forces are exerted on LED package - 14 in opposition to the force of air passing between the floating head and the media. This allows the floating head to fly at a precise distance above the surface of the media.

The embodiment shown in Figure 12 is similar to that of Figure 11, with the exception that the trailing edge of the flexure support structure 90 for LED package 91 is guided in a bracket 92 attached to the leading edge of rotor 94. While a color writer having plural light sources has been described, a monochromatic writer with a single light source may be effected within the spirit and scope of the invention.

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Claims (8)

What is claimed is:

1. A writer comprising: a media support adapted to receive recording media with a radiation-sensitive surface; a floating head with means for projecting at least one beam of radiant energy toward the media support, said floating head having a first surface with a shape to create an airbearing between the surface and an opposed second surface when the floating head is moved relative to the second surface; and a floating head support, one of said medial support and said floating head support being adapted to effect relative movement between the floating head and the radiation-sensitive surfac of received recording media to create an airbearing between the floaing head and the radiation-sensitive surface.

2. A writer as set forth in Claim 1 wherein: the media support is adapted to receive recording media such that the media assumes a cylindrical shape with the radiation-sensitive surface on the inside of the cylindrical shape; and the floating head is inside of the cylindrical shape.

3. A writer as set forth in Claim 1 wherein the means for projecting at least one beam of radiant energy toward the media comprises: at least one LED; and a mask between the LED and the radiationsensitive surface.

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4. A writer as set forth-in Claim 1 wherein the means for projepting at least one beam of radiant energy toward the media comprises:

plurality of LEDs; and mask between the LED and the radiationsensitive surface with a hole in the mask associated with each LED.

5. A writer as set forth in Claim 4 wherein the LED is spaced from the media support by the thickness of the air-bearing plus the thickness of received media.

6. A writer as set forth in Claim 1 wherein the shape of the first surface creates a self-acting air-bearing between the first surface and the opposed second surface.

7. A writer as set forth in Claim 1 wherein the first surface is formed, in part, by foil air dam.

8. A writer as set forth in Claim 7 wherein the foil air dam mechanically locates, by virtue of it's thickness, radiant energy sources in extremely close proximity to received recording media.